SPLIT AMONG TEAM

There were internal disputes within Walker's team about how to best revive his campaign as he slipped in the polls.

Sources close to the campaign described a division between those who worked with Walker on previous campaigns and had strong Wisconsin ties and those whom he brought in from Washington. Campaign manager Rick Wiley was the target of animosity among Walker's close advisers.

Others argued that Walker was not being aggressive enough, falling into a stereotype of Midwestern politeness, and that he needed to take a stronger approach to opponents like Trump.

Walker's lack of experience on the national stage was apparent. He gave shifting answers to questions about illegal immigration and once suggested a wall between the United States and close ally Canada might be in order, in an apparent effort to double down on rivals' calls for a wall on the Mexican border.

Grocery store magnate John Catsimatidis, a billionaire in New York who donated to Walker, said Walker made many mistakes.

"I think the priority is watching out for our southern border and he brought up the Canadian border, and that's not a priority," he said.

Several Republican rivals sent complimentary messages to Walker, some in the hope of gaining the support of his backers.

"I know many people are disappointed with Scott's announcement and I respect what a difficult decision it must have been. He remains one of the best governors in the country," said Rubio.

Who benefits from Walker's exit was a subject of debate within Republican circles with no clear answer, since Walker had appealed to both Christian conservatives and establishment Republicans.

Laurence Goldfarb, the owner of a Great Neck, N.Y. commodities company, said there are two candidates who could attract his donations now that Walker has exited the race - Rubio and Carly Fiorina.

Goldfarb said Walker had been unable to break through such a large field. "You've got one debate a month. You've got to stand out," he said.

Walker was the second Republican to drop out of the race. He follows former Texas Governor Rick Perry, who dropped out on Sept. 11.